The invention relates to a polishing apparatus for polishing a large flat substrate such as, particularly, a silicon wafer, a quartz substrate, a glass substrate, a ceramic substrate, a metal substrate, and a wafer under the production process of an LSI.
FIG. 1 is a perspective view of a prior art polishing apparatus for polishing a large flat substrate. In the figure, 1 is a disk-like polishing table which can horizontally be rotated by a rotating spindle 6. Onto its surface, a polishing cloth 2 which is made of nonwoven fabric such as polyurethane is stuck by an adhesive 21. A disk-like sample holder 3 which is smaller than the polishing table I is located at a position above the polishing cloth 2 and separated therefrom by an adequate distance. The sample holder 3 can horizontally be rotated and moved by a sample holder rotary shaft 5 which is liftable and connected to a driving unit (not shown).
A polishing reagent supply nozzle 7 for ejecting a polishing reagent 8 is fixed at a position which is at the side of the sample holder 3 and above the polishing table 1. A sample B is held to the lower face of the sample holder 3 by an adhesive or a vacuum chuck, and pressingly contacted to the polishing cloth 2 by a polishing load W. While supplying the polishing reagent 8 onto the polishing cloth 2 from the polishing reagent supply nozzle 7, the surface of the sample B is polished by rotating the polishing table 1 and by horizontally rotating and moving the sample holder 3.
Since the polishing cloth 2 is made of nonwoven fabric such as polyurethane, it has a low elastic modulus so as to be easily deformed by a pressure. When a sample is polished by such a polishing apparatus, therefore, the surface of the polishing cloth 2 becomes uneven. To comply with this, an attempt in which a sheet having a thickness of about 0.5 mm is inserted between the polishing cloth 2 and the polishing table 1 has been made. Since the thickness of the polishing cloth 2 is uneven or that of the adhesive 21 is uneven, however, the contacting state between the face of the polishing cloth and the face of the sample to be polished is locally uneven, resulting in a reduced flatness of the face of the sample to be polished. Accordingly, this attempt has been proved not to be effective.
Furthermore, there is a problem in that, since the whole face of the sample to be polished is contacted with the face of the polishing cloth, the periphery portion of the sample is more easily polished than the inner periphery portion and therefore the face of the sample to be polished cannot uniformly be polished. In the case where the load W applied to the sample B is increased so that the contacting state between the face of the polishing cloth and the face of the sample to be polished is uniformalized, there arises a problem in that scratches (scratched portions) are formed on the face to be polished or a polishing distortion is developed, whereby the original properties of the sample are damaged.
When wiring patterns are formed on a wafer substrate in a production process of an LSI and an insulating film is formed to cover the entire surface of the wafer, the surface of the insulating film becomes irregular in accordance with the existence or nonexistence of the wiring patterns. In the case where the insulating film of such a wafer is to be polished, the polishing must be conducted in a macroscopic view point so that the thickness of the insulating film becomes uniform, and in a microscopic view point so that the surface becomes flat. When a soft polishing cloth is used in a prior art polishing apparatus, the elastic deformation of the polishing cloth causes the polishing cloth to deform along the irregularity of the surface of the insulating film, and thus the polishing is done on not only convex portions but also concave portions. FIG. 2 is a diagrammatic section view showing the contacting state between a soft polishing cloth and a wafer. Wirings 84, 84 . . . are formed on a wafer substrate 81, and covered by an insulating film 83. In the case where the surface of such a wafer is to be polished, a soft polishing cloth 82 elastically deforms so as to contact to and polish even concaved portions of the wafer surface, thereby requiring a prolonged time period for making the wafer surface flat (making the level difference of the irregularities zero). Therefore, it is required to increase the thickness of the insulating film as compared with a usual case. Practically, however, there is a limit to increase the thickness of an insulating film, and it is impossible to make the wafer surface completely flat. This produces a problem in that the flatness is low in a microscopic view point.
As a counter measure, a technique in which a very hard polishing cloth may be used in place of a soft polishing cloth may be employed. FIG. 3 is a diagrammatic section view showing the contacting state between a very hard polishing cloth and a wafer. Wirings (not shown) are formed on a wafer substrate 81, and covered by an insulating film 83. In the case where the surface of such a wafer is to be polished, since a very hard polishing cloth 82 has a very high elastic modulus, the polishing cloth contacts to portions which are convex ones in a macroscopic view point, irrespective of the flatness of the wafer surface, and polishes only the contacting portions. Accordingly, the technique has a problem in that the insulating film 83 cannot be polished to a uniform thickness in a macroscopic view point.
It is an object of the invention to uniformalize a contacting state between a face of a polishing cloth and a face of a sample to be polished, thereby improving a uniform polishing and flatness of the sample, and to provide a polishing apparatus and a polishing method using it in which a load applied to the sample is reduced, the smoothness of the sample is improved, and a polishing distortion is reduced.
It is another object of the invention to provide a polishing apparatus and a polishing method using it in which, in a macroscopic view point, a uniform polishing is conducted along a surface of a sample, and, in a microscopic view point, the flatness is improved.
In a polishing apparatus of the invention and a polishing method using the apparatus, an elastic portion is interposed between a polishing table and a polishing cloth. As the elastic portion, an annular disk-like elastic body is interposed so that a face of the polishing cloth contacts a small area of a face of a sample to be polished. This allows the contacting state between the face of the polishing cloth and the face of the sample to be polished to become uniform. Therefore, a polishing is conducted without causing the face of the polishing cloth to apply an excessive load to the periphery portion of the sample.
In another polishing apparatus of the invention and a polishing method using the apparatus, a disk-like elastic body one face of which is spherical is interposed in place of the annular disk-like elastic body. Accordingly, the center portion of the spherical face of the polishing cloth contacts to a face of a sample to be polished, so that the face of the polishing cloth does not apply an excessive load to the periphery portion of the sample, thereby allowing the contacting state between the face of the polishing cloth and the face of the sample to be polished to become uniform.
In a further polishing apparatus of the invention and a polishing method using the apparatus, similarly, a fluid encapsulating portion into which a fluid is encapsulated is interposed between a disk-like polishing table and a polishing cloth covering the polishing table. Accordingly, the fluid encapsulating portion has a disk-like shape one face of which is spherical, and only the center portion of the face of the polishing cloth contacts a face to be polished of a sample, so that the face of the polishing cloth does not apply an excessive load to the periphery portion of the sample, thereby allowing the contacting state between the face of the polishing cloth and the face of the sample to be polished to become uniform. Furthermore, the pressure in the fluid in the fluid encapsulating portion can be controlled so that the polishing is conducted with a contacting state corresponding to the sample.
In a still further polishing apparatus of the invention and a polishing method using the apparatus, a sample-contacting face of a polishing cloth is structured so that resin pellets and/or polishing particles are embedded or attached to a second elastic body. Therefore, the surface of the polishing cloth can deform in accordance with the flatness of a sample in a macroscopic view point so that the surface of the sample is uniformly polished, and convex portions in a microscopic view point of the sample are polished, thereby improving the flatness.
In a still further polishing apparatus of the invention and a polishing method using the apparatus, a sample-contacting face of a polishing cloth is structured so that convex portions, concave portions or groove portions are formed in a second elastic body. Therefore, the surface of the polishing cloth can deform in accordance with the flatness of a sample in a macroscopic view point so that convex portions in a microscopic view point of the sample are selectively polished.
In a still further polishing apparatus of the invention and a polishing method using the apparatus, the above-mentioned elastic portion is interposed, and a sample-contacting face of a polishing cloth is structured so that resin pellets and/or polishing particles are embedded or attached to a second elastic body, or that convex portions, concave portions or groove portions are formed in the second elastic body. Therefore, the contact between the face of the sample to be polished and the polishing cloth becomes uniform, the surface of the sample is uniformly polished in a macroscopic view point, and convex portions are selectively polished in a microscopic view point, thereby improving the flatness.